This invention relates to a tubular aluminum electrolytic capacitor having a metal can housing and anode and cathode leads extending in one axial direction from the housing and a third dummy lead extending in the other axial direction from the housing.
Aluminum electrolytic capacitors of the wound foil type are typically housed in a cylindrical aluminum can. For low profile mounting to a printed circuit board, the can is laid on its side, and many such capacitor packages have an anode lead extending through a lead-to-can seal at one can end and the cathode lead extending in the opposite direction through a lead-to-can seal at the other can end. Such capacitor packages have their two leads bent at right angles and threaded through holes provided therefor in a printed circuit board. This assembly is then wave soldered.
However, it is substantially less expensive in manufacturing to make both anode and cathode leads extend in the same direction through one seal at one can end. To prevent the other can end from vibrating or from moving when inadvertantly being pushed, a third wire lead is welded to the closed end. That lead is also bent and mechanically soldered at a printed circuit board hole provided therefor. This construction also has the advantage that the more closely parallel anode and cathode leads and printed circuit board wiring provides a substantial improvement in capacitor high frequency response. The package is described more fully in the Engineering Bulletin No. 3453, copyright 1983, Sprague Electric Company, Lexington, Mass.
Both of these capacitor packages conventionally have an anode lead that is longer (e.g. by 0.25 inch) than the cathode lead. This makes it possible to visually distinguish, and to distinguish by automatic means, e.g. by mechanical feelers, the anode from the cathode lead wires. These leads may be cut to equal lengths just prior to printed wire board assembly. Such single ended capacitors are being produced by highly automatic means at a very low cost all over the world. They are also being inserted into printed circuit boards and then automatically wave soldered.
Capacitors 10 of this kind may be connected electrically and mechanically to a printed wiring board 12 as indicated in FIGS. 1, 2 and 3. In these figures, the capacitor 10 is kept in position in the printed wiring board 12 by the three leads 14, 16 and 18 having been threaded through holes 20, 22 and 24, respectively, in the board ready for wave soldering to copper lands (not shown) that are bonded to the underneath side of the board.
This invention addresses a problem that is experienced after positioning on the printed wiring board and before the wave soldering step. There is a tendency for the cylindrical body to roll when the carrier that brings the printed circuit board to the wave solder machine either lists, hesitates, or experiences sudden lateral movement for any reason. At least one of the anode or cathode leads tend to withdraw from the printed wiring board hole enough so that the solder does not reach it and neither electrical nor mechanical connection is effected at wave soldering.
It is an object of this invention to provide an improved low cost aluminum electrolytic package that, when seated on a printed wiring board ready for soldering, is less likely to roll so that the anode or cathode lead is withdrawn far enough from its respective printed-wiring-board hole that it is not connected at soldering.